Consolidated Statements Of Changes In Stockholders' Equity And Comprehensive Income (USD $) In Thousands, except Share data	Common Stock [Member]	Common Stock, Held In Treasury, At Cost [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Benefits Liability Net Of Tax [Member]	Cumulative Foreign Currency Exchange [Member]	Net Unrealized Holding Gains On Investments, Net Of Tax [Member]	Total
Balances at Dec. 31, 2008	$ 657		$ 435,581	$ 814,873	$ (13,339)	$ 1,288		$ 1,239,060
Balances, shares at Dec. 31, 2008	65,658,142
Net income				52,995				52,995
Other comprehensive (loss) income					(2,517)	3,063		546
Total comprehensive income								53,541
Stock options exercised			879					879
Stock options exercised, shares	55,401
Stock-based compensation, net of tax on stock options exercised	3		6,009					6,012
Stock-based compensation, net of tax on stock options exercised, shares	266,408
Dividends paid				(14,510)				(14,510)
Balances at Dec. 31, 2009	660		442,469	853,358	(15,856)	4,351		1,284,982
Balances, shares at Dec. 31, 2009	65,979,951
Net income				221,393				221,393
Other comprehensive (loss) income					3,528	944		4,472
Total comprehensive income								225,865
Stock options exercised	2		3,745					3,747
Stock options exercised, shares	173,014
Stock-based compensation, net of tax on stock options exercised	1		6,489					6,490
Stock-based compensation, net of tax on stock options exercised, shares	103,179
Dividends paid				(16,014)				(16,014)
Balances at Dec. 31, 2010	663		452,703	1,058,737	(12,328)	5,295		1,505,070
Balances, shares at Dec. 31, 2010	66,256,144
Net income				258,966				258,966
Other comprehensive (loss) income					(2,815)	(407)	1,185	(2,037)
Total comprehensive income								256,929
Common stock repurchased		(2,518)						(2,518)
Stock options exercised	3		5,341					5,344
Stock options exercised, shares	274,872							274,872
Stock-based compensation, net of tax on stock options exercised			9,752					9,752
Stock-based compensation, net of tax on stock options exercised, shares	70,893
Dividends paid				(18,265)				(18,265)
Balances at Dec. 31, 2011	$ 666	$ (2,518)	$ 467,796	$ 1,299,438	$ (15,143)	$ 4,888	$ 1,185	$ 1,756,312
Balances, shares at Dec. 31, 2011	66,601,909